Ataxia-Telangiectasia (A-T) is a multi-systemic, recessively inherited disorder characterized primarily by early onset cerebellar ataxia and telangiectasia, from which the disease name is derived. In addition, patients also exhibit a number of other clinical symptoms including increased susceptibility to cancer (lymphomas, leukemia, brain tumors), immunodeficiency, insulin-resistant diabetes, chromosomal instability, sensitivity to ionizing radiation, susceptibility to bronchopulmonary disease, and the nearly complete absence of a thymus. A-T is a progressive and ultimately fatal disease, with most patients dying in their early twenties. Current treatments for A-T are directed primarily toward the management of symptoms. Physical and speech therapy may improve the daily lives of patients, and 3-globulin injections can be given to support the immune system. However, no treatment is currently directed at the underlying defect. The development of improved therapies for A-T is currently limited by the lack of an animal model that fully and accurately recapitulates the multi-systemic nature of this disease. A number of mouse models of A-T have been developed by the targeted disruption of the mouse Atm gene and have proved invaluable for studying some aspects of ATM function and A-T disease. However, no single mouse model fully replicates the complex clinical symptoms observed in human disease, and more importantly, none of the mouse models develop the severe neurological phenotype that is the hallmark of human A-T. The failure of mouse models to develop the classical symptoms of A-T is likely the result of physiological, anatomical, and developmental differences between the two species. In contrast, pigs may serve as a better model in which to study human disease because their development, anatomy, and physiology are more closely related to that of humans. Given that the development and anatomy of the pig brain more closely resembles that of humans than mice, mutations in the porcine ATM gene may result in many of the same neurological changes that are observed in A-T patients. The ultimate goal of this proposal is to develop and commercialize a porcine model of A-T by disrupting the ATM gene. We intend to accomplish this in two steps by combining gene targeting and somatic cell nuclear transfer (SCNT). This proposal specifically outlines the development of porcine fibroblasts with mutated ATM alleles. Gene targeting vectors will be constructed to disrupt the endogenous porcine ATM gene in a region frequently mutated in patients. Porcine fetal fibroblasts will be infected with a virus carrying the ATM targeting vectors. Our plans for generating properly targeted cells are designed to maximize the frequency of homologous recombination, minimize random integration, and minimize the number of cell passages before targeted cells are harvested. Subsequent work will use these cells for somatic cell nuclear transfer to produce ATM-targeted pigs and the subsequent characterization and validation of the pigs. This animal model will provide the academic and commercial research communities an opportunity to better understand the consequences of ATM dysfunction and the pathogenesis of A-T disease, and to develop and test new therapeutic strategies. PUBLIC HEALTH RELEVANCE: Project Narrative This proposal specifically outlines the development of porcine fibroblasts with mutated ATM alleles as a first step towards a new model of the human disease, Ataxia-Telangiectasia. Subsequent work will use these cells for somatic cell nuclear transfer to produce affected pigs followed by characterization and validation of the animal model. This project is relevant to the NIH's mission because it will provide a resource to stimulate discovery, therapeutic application, and the development of new diagnostic tools.